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wireless relays

I don't have access to cable or dsl. My friend down the

> road (we are in a rural hilly area north of Knoxville TN) > does have cable. It stopped about 1/2 mile from my house. I > am exploring some way to network with his house to get > higher speed. I discussed it with the cable company and was > informed that due to cost they would not be extending it my > way any soon and the person I talked to didn't see any > problem with the sharing, since they would/could not > provide it.

Extending CATV about 1/2 mile is not a big deal. At worst, you'll need a line amplifier. Instead of connecting to your friend, is there someone near the end of the cable that can be convinced to attach a connection?

I am still looking into some type of wire connection, it is > about 1.2 miles.

Lots of ways to do 1.2 miles. The easiest is 2 twisted pair and a pair of SDSL modems. Not all SDSL modems will work. I have a list somewhere. The catch is that you may be limited to about 3Mbits/sec thruput.

I am going to check with BellSouth about > getting a dry pair that is looped out here somewhere. If it > goes to the CO, it will be too far to be of any use. I am > about 10 mitles from there. But from what I have read, > this is probably a no-go.

Good luck. We can't get dry pairs in SBC country at all. Totally impossible including alarm companies. I've tried. All drops go via the CO. Sorry.

I am also going to check with the utility company about > stringing my own cable. Don't know how that will go, or > what type of expense I am looking at, but asking is free.

I've done it for short distances without permission. They don't like it but it's too big a bother to tear them all down. As long as it's done professionally, they don't seem to care. I've also strung fiber legally on the former Pacific Bell poles. The cost was nominal (about $2/pole) to the utilities, but the insurance costs was really awful. Something like $20,000/year for $10million in liability. That's how they keep independents off the poles legally.

That leaves me wireless. I can get line of sight from the > top of the ridge behind me. I own the property but there is > no power anywhere around.

No problem. Most wireless repeaters only burn about 5 watts maximum. A gel cell and a solar charger can handle that.

The idea of the passive repeaters > sound really good.

No. They don't work. Please re-read whatever I wrote. The beamwidth necessary at both ends is very small. The reflector will by necessity be VERY big.

And I see posts all over the place > recommending them, but your math and reasoning looked > pretty sound at ruling it out in the basic case. > Are these people recommending something that just sounds good but they > have not actually tried to get it to work?

I've gotten it to work under limited conditions. One used a 4ft diamter dish at each end. The reflector was a solid piece of 3x6ft aluminium sheet metal. Losses were horrible, but it was good enough. Big problem in the morning when water condensed on the reflector and screwed up the signal.

In my case I would estimate 1 mi from the relay to my friend > (A) and . 5 mi from the relay to me (B). I used the page you > referred to to do some calculations, but am not sure if I > did things correctly. If I wanted a passive repeater to work, > how much power would I need if I had 24dbi antennas all > around? Is it feasible with amplifiers?

Maybe. Let's see your calculations and I'll check them. However, I would prefer you re-post your question in alt.internet.wireless so I can deal with it at my leasure.

How about if I put a bi-directional amplifier between the > relay antennas and powered that with a battery/solar > charger. That should require such little power I don't > think it would be a problem. A 250mw doesn't seem too expensive.

A 250mw (24dBm) amplifier at each end will improve the signal over the typical +15dBm radio by about 9dB. That's quite a bit and will help. However, the beamwidth will kill you no mattery how much power you have. A 6degree beamwidth 24dBi antenna at 0.6 miles (3200ft) will be over 300ft wide. Got a 300ft wide reflector? Cut the area in half and you lose 3dB. Half again, another 3dB. Do it often enough and you have no signal left.

Reply to
TKMitchell
Loading thread data ...

My question about the amplifier is in putting it in the field with the relay. Instead of having a totally passive relay, hook up a bidirectional amplifier between the 2 antennas. It seems that shooting the 1 mile with 2 good antennas. But it has been shown there is not enought signal to feed into the next antenna as a passive relay. Would amplifying the signal then feeding that into the second antenna provide enough power to be usable.

radio - antenna -------------------- antenna - amp - antenna

-------------------- antenna - radio

But even if this works, I ran across another fact that might be my downfall. I read a post discussing the ACK time for 802.11 and they showed how 1 mi was about the limit due to timing. I couldn't tell if they meant that just for the 11MB or also applied to the lower speeds.

As for me if I can get 2MB or better I would be happy.

Reply to
TKMitchell

Ok, let's do the math.

Let's pretend we have a symmetrical bi-directional amplfier with perhaps 15dB of gain. I don't know if such a thing exists, but you can use Google to find something. Remember, it has to be symmetrical, not a bi-directional amplifier that will belch lots of power in one direction, and just run the receiver in the other. It also has to have it's own transmit/receive switching mechanism to switch direction. Let me know if you find something similar.

Running it through the link calculations at: |

formatting link
would guess we have:

TX power = +17dBm TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors) TX ant gain = 24dBi parabolic dish Distance = 0.6 miles RX ant gain = 24dBi parabolic dish RX coax loss = 4dB (same at other end) RX level = unknown

Plugging into:

formatting link
get an RX level of -44.8dBm. With a 15dB amplifier, the tx level is now: -44.8 +15 = -29.8dBm or -30dBm (close enough)

Now, we do the other half of the link: TX power = -30dBm TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors) TX ant gain = 24dBi parabolic dish Distance = 0.6 miles RX ant gain = 24dBi parabolic dish RX coax loss = 4dB (same at other end) RX level = unknown

Plugging into:

formatting link
we get a receive level of about -90dBm.

In order for such a link to function, we need a minimum fade margin of

20dB. Less will work, but not very reliably. The basic receiver sensitivity is about -84dBm (at 11Mbits/sec) which yields a fade margin of -6dB. That's 26dB short of being useable. If you've got a way of gaining 26dB more gain in there, it might work. A 1 watt (maximum legal) power amplifier on both ends will gain about 13dB but that's still not enough.

Conclusion: Unless I screwed up the math (it happens), a bi-directional amplifier won't work.

It is my understanding that the timing limit is about 10 miles. There are numerous links running between 1 mile and further, that work just fine.

Find a Wi-Fi repeater, range extender, or whatever. Install on the hilltop. Solar power with a gel cell, charge controller, and possibly a DC to DC regulator. Most such repeaters suck about 5 watts. Try bashing the numbers into my solar calculation speadsheet at:

formatting link
yellow numbers are the one's you can tweak. I'll help after I throw all the visitors out of my palatial office.

Reply to
Jeff Liebermann

My question about the amplifier is in putting it in the field with the relay. Instead of having a totally passive relay, hook up a bidirectional amplifier between the 2 antennas. It seems that shooting the 1 mile with 2 good antennas. But it has been shown there is not enought signal to feed into the next antenna as a passive relay. Would amplifying the signal then feeding that into the second antenna provide enough power to be usable.

radio - antenna -------------------- antenna - amp - antenna

-------------------- antenna - radio

But even if this works, I ran across another fact that might be my downfall. I read a post discussing the ACK time for 802.11 and they showed how 1 mi was about the limit due to timing. I couldn't tell if they meant that just for the 11MB or also applied to the lower speeds.

As for me if I can get 2MB or better on the link I would be happy.

Reply to
TKMitchell

My question about the amplifier is in putting it in the field with the relay. Instead of having a totally passive relay, hook up a bidirectional amplifier between the 2 antennas. It seems that shooting the 1 mile with 2 good antennas. But it has been shown there is not enought signal to feed into the next antenna as a passive relay. Would amplifying the signal then feeding that into the second antenna provide enough power to be usable.

radio - antenna -------------------- antenna - amp - antenna

-------------------- antenna - radio

But even if this works, I ran across another fact that might be my downfall. I read a post discussing the ACK time for 802.11 and they showed how 1 mi was about the limit due to timing. I couldn't tell if they meant that just for the 11MB or also applied to the lower speeds.

As for me if I can get 2MB or better on the link I would be happy.

Reply to
TKMitchell

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